Hybrid control circuit

ABSTRACT

A device for controlling a capacitive charge, in particular a piezoelectric actuator ( 2 ) has a signal generator ( 6 ) which is used to control a first end step ( 1 ) which is used to produce a discrete signal on the capacitive charge. Device has a second end step ( 3, 4 ) which is used to generate a continuous signal on the capacitive charge. A counter-coupling of a deviation of an actual discrete signal is produced by a continuous signal required on the capacitive charge.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApplication No. PCT/EP2005/055341 filed Oct. 18, 2005, which designatesthe United States of America, and claims priority to German applicationnumber 10 2004 052 248.0 filed Oct. 27, 2004, the contents of which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a device for controlling a capacitiveload, especially a piezoelectric actuator, featuring a signal generatorfor controlling a first end stage or a device to produce a discretesignal at the capacitive load.

BACKGROUND

To enable piezoelectric actuators to be used in applications ofautomotive technology, building technology and automation technologycontrollers are needed which can generate voltage-time functions withsteep edges and high final voltages at capacitive loads. To achieve ahigh efficiency switching end stages are used to control theseactuators. The discontinuous supply of energy however results in a highlevel of harmonics and deviation of the actuator deflection from itssetpoint function. The advantages of a high level of efficiency, lowerrise times and higher final voltages are set against a greater harmonicproportion and deviation from the required value. In particular, whenthe method is used to control the actuators of a piezo motor, a highproportion of harmonics produces higher noise levels. A potentialadvantage of the piezoelectric drive, the silent idling, thus remainsunused.

Control deviations and harmonics which are caused by discrete energypackets from switched end stages can be reduced by adapting the endstages to the piezo-electric actuators and to the time functions to beachieved.

Limits are imposed on this reduction however by the dynamic range of thecircuits and components used, as well as by the effort involved incircuit construction. Thus “charge packets” generated by a switching endstep can only be scaled within limits. An end stage with small risetimes does not create charge packets of the given small size. Apredetermined required value is thus not achieved without a deviation inregulation. Harmonics, created by the clocked operation and the highdistortion factor of the generated control function resulting from thecontrol deviations can in fact be attenuated by filtering. However,especially if useful and harmonic frequencies lie close together in thefrequency band or if high noise levels are to be attenuated, the outlayinvolved is extraordinarily high and the efficiency is reduced.

SUMMARY

A device can control capacitive loads in such a way that deviations ofthe signal size at the capacitive load occurring in respect of apredetermined function or deviations of the actuator deflection and aharmonic level are effectively reduced by comparison with conventionalcontrol circuits. According to an embodiment, such a device forcontrolling a capacitive load may comprise a signal generator forcontrolling a first end stage for producing a discrete signal at thecapacitive load, a second end stage for creating a continuous signal atthe capacitive load, and a comparison device for controlling the secondend stage, wherein the comparison device compares a required continuoussignal of the signal generator with an actual discrete signal at thecapacitive load.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained in greater detail below usingexemplary embodiments illustrated in conjunction with the figures. Thefigures show:

FIG. 1 shows a schematic overall layout to illustrate the principleaccording to an embodiment;

FIG. 2 shows a first exemplary embodiment of a device;

FIG. 3 shows a second exemplary embodiment of a device;

FIG. 4 shows a simulation circuit with a charge generator and acontinuous regulator;

FIG. 5 shows a simulation circuit without a continuous regulator;

FIG. 6 shows voltage-time functions of a circuit depicted in FIG. 4(regulated) and FIG. 5 (unregulated).

DETAILED DESCRIPTION

Using a continuous signal corresponding to a setpoint function, a signalgenerator generates a discrete signal at the capacitive load at a firstend stage or device. By means of a second end stage or device, acontinuous signal is generated at the capacitive load depending on asetpoint function of the signal generator and an actual discrete signalat the capacitive load. This means that there is a counter coupling of adeviation of an actual discrete signal from a required continuous signalat the capacitive load. The deviation is detected using a comparisondevice controlled by the second end stage or device. Static signals inparticular are signals with continuous times and values. Discretesignals can be discrete in time or value.

A precise and low-harmonic control of a piezoelectric actuator iseffected by a combination of a device for creating discrete signals anda device for creating a continuous signal. The discrete signal isespecially a time-discrete signal and moreover especially a clocksignal, in particular with constant or variable end level and/orvariable duration. Especially when piezo-electric actuators are used theclock signals are voltage-time functions with steep edges and high finalvoltages. The continuous signal is especially a time-continuous signal.Because of the counter-coupling of a deviation of the actual discretesignal from a setpoint function by means of the continuous signalgenerated by the second signal generator, distortion factor and harmoniclevel can be effectively reduced.

In accordance with an advantageous embodiment the signal generator, forcontrol of the first and the second end stage, creates at least onesetpoint function, especially a continuous signal.

The comparison device can additionally feature an amplifier, especiallyfor amplification of the difference between the required continuoussignal of the signal generator and the actual discrete signal at thecapacitive load. Using a comparison device and possibly an amplifier,the actual value of the discrete signal can be compared at thecapacitive load with the required value corresponding to a setpointfunction. The required value is supplied by the signal generator of thecomparison device. After the control signal has been amplified ifnecessary, the second end stage is controlled in accordance with theresult of the comparison. An operational amplifier can be preferred as asuitable comparison device and/or amplifier.

In accordance with an advantageous embodiment the first end stage isprovided as a regulated clocked end stage. The first end stage can alsobe embodied unregulated.

In accordance with a further advantageous embodiment the second endstage with a comparison device can provide a fast controller withcorresponding time constants.

Furthermore it is especially advantageous for a measured value recorderto be provided at the capacitive load for detection of the actual valueof the signal variable to be used for regulation. The measured valuerecorder can for example detect voltage, current, charge or energy orpower. To this end the measured value recorder is especiallyelectrically connected in series or parallel to the capacitive load.Measured values can also be detected using a non-contact method.

In accordance with advantageous embodiments, the signal generator candirectly or indirectly provide a charge, a voltage or general energy atthe capacitive load via a corresponding end stage.

It is further advantageous for the second end stage to have a variablevoltage source and a capacitor, electrically connected to each other inseries or in parallel.

To compensate for outside effects which can result in departure from theregulation range of the second end stage, a compensation element isadvantageously electrically connected to the capacitive load or to thecapacitor.

It is especially advantageous for the compensation element to be aresistor or a switch electrically connected in parallel to thecapacitive load or the capacitor.

FIG. 1 shows a schematic diagram of the overall layout for actuatorcontrol according to an embodiment. The layout consists of a signalgenerator 6, a first end stage 1 (charge generator), an analog regulatormade up of components 7, 3, 4 and a load 2.

The signal generator 6 creates the setpoint function which is coarselysimulated by the first end stage 1. A measured value recorder (notshown) on the actuator 2 determines the actual value to which regulationis to be undertaken. These values can for example be voltage, charge orenergy. The actual value is fed to the comparison device/amplifier 7which compares the signal to a setpoint value generated by the signalgenerator 6 and creates a control variable. The variable voltage source3 is controlled with this value, whereby a charge is moved from thecapacitor 4 to the actuator 2. This corrects the error which hasoccurred.

The first exemplary embodiment shown in FIG. 2 effectively solves thetechnical problems produced with conventional devices. The disadvantagesof the clocked end stage are likewise compensated for throughcombination of a clocked end stage and an end stage with time-continuousoutput signal. Regulation deviations and harmonics are compensated forby the time-continuous controlling over a large bandwidth.

Likewise, by the circuit depicted in FIG. 2, the two concepts are mergedby utilizing the respective advantages. The clocked end stage 1 in thiscase creates the basic time function of the charge, energy, power,current or voltage at a piezoelectric actuator 2 specified by the signalgenerator 6. FIG. 2 shows a charge generator 1 as an exemplaryembodiment for a clocked end stage. Through a second end stage or asecond signal generator, consisting of a branch with a variable voltagesource 3 and a capacitor 4, small amounts of charge are taken from orfed to the piezoelectric actuator 2. The variable voltage source 3 iscontrolled using a control loop sensitive to piezo charge, energy orvoltage. Since the requirements for the voltage increase and thecurrents are small by comparison with a clocked end stage, high limitfrequencies of the control loop can be reached. This means that thecontinuous regulator is able to compensate for harmonics and deviationsfrom the required value over a large bandwidth.

In accordance with a second exemplary embodiment depicted in FIG. 3, avariable voltage source 3 is arranged electrically in parallel to anactuator 2. Actuator 2 and variable voltage source 3 are likewiseconnected electrically in parallel to a capacitor or to a capacitance 4.A device in accordance with FIG. 3 functions in a comparable manner tothe device depicted in FIG. 2, however, by contrast with FIG. 2, thereference potential of the actuator 2 is moved. The capacitance 4accepts the charge moved from it.

An element 5 in FIGS. 2 and 3 is used to compensate for outside effectswhich can lead to departures from the range of regulation of thecontinuous regulator or of the second signal generator. In the simplestcase element 5 is an electrical resistor. If the actuator 2 iscontrolled cyclically, the element 5 can be embodied as a switch whichdischarges the capacitances 2 and 4 at each zero crossing of thesetpoint function. In this case the voltage source 3 is also regulatedto zero at zero crossing.

The effective principle according to an embodiment has been verifiedwith the aid of simulations and on the basis of a test setup. Thesimulation is documented by FIG. 4, FIG. 5 and FIG. 6.

FIG. 4 shows the simulation circuit for a hybrid end stage with a chargegenerator (pulsed current source) and a continuous (analog) controller,essentially consisting of a fast operational amplifier.

The circuit depicted in FIG. 5, which is provided without a continuouscontroller, serves as a comparison to FIG. 4. This circuit creates theunregulated voltage-time function V(unregulated) shown in FIG. 6 (seelower timing diagram). The jumps caused by the voltage generator areclearly visible here. The time function of the required value V(reqval),which is a triangular function, is shown in the same diagram.

By using the regulated circuit according to FIG. 4 the deviations ofvoltage over the load from the required voltage are effectively reduced.The voltage-time function V (analog regulator) confirms the effect bythe small deviations from the required function (see FIG. 6; uppertiming diagram).

In practice the jumps created by the clocked end stage are smaller andthe final voltages higher. The coupling-in of the continuous regulator(obtaining the actual value) is then undertaken using a voltage divider.The performance under these conditions could also be confirmed on thebasis of a test setup.

1. A device for controlling a capacitive load comprising: a signalgenerator for controlling a first end stage for producing a discretesignal at the capacitive load, a second end stage for creating acontinuous signal at the capacitive load, a comparison device forcontrolling the second end stage, wherein the comparison device comparesa required continuous signal of the signal generator with an actualdiscrete signal at the capacitive load.
 2. The device according to claim1, wherein the signal generator, for controlling the first end stage andsecond end stage, creates at least one setpoint function.
 3. The deviceaccording to claim 1, wherein the comparison device additionallycomprises an amplifier.
 4. The device according to claim 1, wherein thefirst end stage is provided as a regulated clocked end stage.
 5. Thedevice according to claim 1, wherein the second end stage has a timeconstant and by means of its time constants and the comparison device,provides a fast controller.
 6. The device according to claim 1, whereina measured value recorder is provided at the capacitive load fordetection of the actual discrete value of the signal variable to whichthe signal is to be regulated.
 7. The device according to claim 1,wherein the signal generator provides a charge, a voltage or generalenergy.
 8. The device according to claim 1, wherein the second end stagefeatures a variable voltage source and a capacitor.
 9. The deviceaccording to claim 4, wherein an element to compensate for outsideeffects is electrically connected to the capacitive load or thecapacitor.
 10. The device according to claim 9, wherein the element tocompensate for outside effects is a resistor or a switch electricallyconnected in parallel to the capacitive load or the capacitor.
 11. Amethod for using a device comprising: a signal generator for controllinga first end stage for producing a discrete signal at the capacitiveload, a second end stage for creating a continuous signal at thecapacitive load, a comparison device for controlling the second endstage, wherein the comparison device compares a required continuoussignal of the signal generator with the actual discrete signal at thecapacitive load, the method comprising the steps of: controlling acapacitive load with a discrete signal by a signal generator and a firstend stage outputting discrete signals, providing a negative feedback ofa deviation of an actual discrete signal from a required continuoussignal undertaken by means of a continuous signal of a second end stage.12. A piezo electric actuator for controlling a capacitive loadcomprising: a signal generator coupled with a first end stage outputtinga discrete signal, a second end stage outputting a continuous signal,wherein the capacitive load receives a sum of said discrete signal andsaid continuous signal, a comparator having an output coupled with thesecond end stage and having a first input receiving a requiredcontinuous signal of the signal generator and a second input receivingan actual discrete signal at the capacitive load.
 13. The deviceaccording to claim 12, wherein the signal generator generates acontinuous signal as a setpoint function.
 14. The device according toclaim 12, wherein the comparison device comprises an amplifier.
 15. Thedevice according to claim 12, wherein the first end stage is provided asa regulated clocked end stage.
 16. The device according to claim 12,wherein the second end stage has a time constant and provides a fastcontroller by means of its time constants and the comparison device. 17.The device according to claim 12, wherein a measured value recorder isprovided at the capacitive load for detection of the actual discretevalue of the signal variable to which the signal is to be regulated. 18.The device according to claim 12, wherein the second end stage comprisesa variable voltage source and a capacitor.
 19. The device according toclaim 15, wherein an element to compensate for outside effects iselectrically connected to the capacitive load or the capacitor.
 20. Thedevice according to claim 19, wherein the element to compensate foroutside effects is a resistor or a switch electrically connected inparallel to the capacitive load or the capacitor.